Chum Salmon Populations Research Articles

Genetic differentiation among seasonally distinct spawning populations of chum salmon, Oncorhynchus keta

Fry from three Vancouver Island chum salmon populations were reared under identical conditions from egg onward to determine if genetic divergence occures among populations that spawn in different seasons. Comparisons of genetic traits, such as incubation rate and external morphology, revealed significant differences between the autumn spawning stock and the two winter spawning stocks. At constant 6°C, simulated autumn spawning regime and simulated winter spawning regime incubation rates of winter stock embryos were more rapid than those of the autumn spawning population. However, genotype-environment interaction occurred at constant 10°C such that autumn stock embryos incubated more rapidly. Discriminant analysis of 10 morphometric features of the progeny separated groups corresponding to the three stocks. Environmental factors were important as the key characteristics of separation varied with temperature regime. Both genotype and genotype-environment interactions contribute to divergence among seasonally distinct spawning populations.

Distribution, migration and possible origins of genetically different populations of chum salmon Oncorhynchus keta along the eastern coasts of northern Japan.

Distribution and migration paths of chum salmon populations distributed in the waters northeast off Japan from autumn to spring were examined based on allelic frequencies and some biological characteristics. Two distinct maturity classes, namely maturing and immature fish were observed among autumn collections and significant allelic differences were found between them. The allelic differences of maturing fish as well as their tag recovery data indicated that maturing chum salmon population mainly consists of the fish returning to Japanese rivers. Since immature collections taken in autumn and maturing collections taken in spring during their northward shifts were statistically very similar, it is considered that the former has a link with the latter. Allelic frequencies of these fish corresponded better with known frequencies of populations of the Amur River area in the Soviet Union. The above as well as minimal tagging data suggest that the immature fish wintercd in southern waters and subsequently migrated to the north to approach the Amur River area as maturing fish.

Heterozygosity and morphological variability of chum salmon (Oncorhynchus keta) in southern British Columbia.

We compared variability in two meristic and six morphometric characters with heterozygosity within and among 27 populations of chum salmon (Oncorhynchus keta) in southern British Columbia. Among individuals, there was no relationship between levels of heterozygosity at 10 electrophoretic loci and degree of meristic or morphometric variation. Decreased morphological variance was not associated with increased heterozygosity. Morphological variance and heterozygosity did not change with age for chum salmon maturing at three to five years of age. Among populations of chum salmon, increased levels of average heterozygosity were not associated with decreased variance of morphometric or meristic characters. Our results do not support the hypothesis that more heterozygous individuals show less phenotypic variability than more homozygous ones due to a canalization of morphology during development. Genetic distances between pairs of chum salmon populations were significantly correlated with pairwise Mahalanobis distances derived from meristic, but not from morphometric characters. Chum salmon are morphometrically adapted to the natal stream environment, whereas biochemical and meristic characters in these populations may be less affected by local selective forces.

Species Selective Predation on Juvenile Pink (Oncorhynchus gorbuscha) and Chum Salmon (O. keta) by Coho Salmon (O. kisutch)

Predation on juvenile pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta) by yearling coho (O. kisutch) was studied in marine enclosures in Masset Inlet, B.C. These experiments demonstrate that coho prey selectively upon pink salmon even when chums are both significantly smaller and more abundant than pink salmon. Reexamination of the results of similar experiments conducted in Burke Channel, B.C., also confirms that mortality was biased towards pink salmon. Prey species may be more important than prey size for coho that prey upon mixed populations of pink and chum salmon during early sea-life.

Genetic structure of chum salmon Oncorhynchus keta river populations.

Chum salmon populations which distributed extensively from North America via the U. S. S. R. to Japan were investigated. Several regional populations consisting of adjacent river populations were identified from the gene frequency data. It is presumed that the accumulation of the genetic intermingling for generations lead to genetic similarity among river populations within one region. Chum salmon population is unique among the species of genus Oncorhynchus in having several regional populations. This characteristic presents a striking contrast to sockeye salmon and others in which the genetic isolation of river populations is more evident.

Geographical distribution of allelic variations of enzymes in chum salmon Oncorhynchus keta, river populations of Japan and the effects of transplantation.

Allelic frequencies of fourteen polymorphic loci were compared among chum salmon populations returning to forty-three rivers in Japan. The study on genetic similarity revealed two major clusters of (1) Okhotsk and Nemuro and (2) East of Cape Erimo regional populations in Hokkaido and (1) northern and (2) southern regional populations both on the Pacific coast and the Japan Sea coast of Honshu. The division occurs at the middle of Iwate Prefecture on the Pacific coast and at the northern part of Niigata Prefecture on the Japan Sea coast. The common genetic feature is still observed despite the frequent transplantations attempted to date, which suggests there is no noticeable effects of planting.

サケとニジマスのリンゴ酸脱水素酵素に関与する重複遺伝子と変異

Supernatant malate dehydrogenase (S-MDH) isozymes of chum salmon and rainbow trout were examined by starch gel electrophoresis. Three types of B-subunit isozyme patterns were demonstrated for 396 specimens of chum salmon captured in nine rivers, and four types for 420 of rainbow trout from six hatcheries. On the bases of the occurrence of three isozymes at distinctly asymmetrical ratios in heterozygote variants and the frequencies of phenotypes in the populations examined, it was suggested that each of these two species possesses duplicate genetic loci producing dimeric isozymes, which are composed of subunits B' and B in rainbow trout, and B and B" in chum salmon, under the control of corresponding alleles. The gene frequencies of B allele in the rainbow trout populations and the frequency of B" allele in the chum salmon populations were respectively .103 and .056 at most: 65 to 95 percent of rainbow trout exhibited a single isozyme consisting of B' subunit, and more than 82 percent of chum salmon exhibited one consisting of B subunit. The demonstration of duplicate loci for B-subunit isozyme of S-MDH in both species provides additional support for the tetraploidy hypothesis of salmonids.

Principles Affecting the Size of Pink and Chum Salmon Populations in British Columbia

In pink salmon (Oncorhynchus gorbuscha) the survival during the freshwater phases of the life-cycle has been found to vary from about 1 to 24 per cent of available eggs. Natural survival during marine existence is considered to average about 5 per cent. In the central region of the British Columbia coast the annual catch averages about 60 per cent of the adult fish. Populations maturing in "even" and "odd" years vary in size independently. Fluctuations in level of stock originate mainly in fresh water.Population levels and changes are determined by the combined effects of three types of mortality: (a) mortality which becomes relatively heavier as populations increase in density (compensatory); (b) mortality which becomes relatively heavier as populations decrease in density (depensatory); (c) mortality which is independent of density (extrapensatory). Compensatory mortality is especially identified with the, period of spawning and incubation. Depensatory mortality is considered to occur mainly during the period of fry migration and to be due to predation. Extrapensatory mortality may occur at any stage; it is most variable during the period between entrance of the adults into fresh water and emergence of the free-swimming fry.Populations of chum salmon (O. keta) are controlled by similar influences. Effects are modified by higher egg-production and a less rigid life-span than in the pink salmon.